A list of polygons that belong to this isoline. An isoline can consist of multiple polygons. For example, islands that can be reached by a ferry are included. Each island is then represented as a separate polygon. However, in most cases only a single polygon is included. Gets a list of polygons that belong to this isoline. An isoline can consist of multiple polygons. For example, islands that can be reached by a ferry are included. Each island is then represented as a separate polygon. However, in most cases only a single polygon is included.